MostSinorhizobium melilotiExtracytoplasmic Function Sigma Factors Control Accessory Functions

Abstract

Fixed (reduced) soil nitrogen plays a critical role in soil fertility and successful food growth. Much soil fertility relies on symbiotic nitrogen fixation: the bacterial partner infects the host plant roots and reduces atmospheric dinitrogen in exchange for host metabolic fuel, a process that involves complex interactions between the partners mediated by changes in gene expression in each partner. Here we test the roles of a family of 11 extracytoplasmic function (ECF) gene regulatory proteins (sigma factors [σs]) that interact with RNA polymerase to determine if they play a significant role in establishing a nitrogen-fixing symbiosis or in responding to various stresses, including cell envelope stress. We discovered that symbiotic nitrogen fixation occurs even when all 11 of these regulatory genes are deleted, that most ECF sigma factors control accessory functions, and that none of the ECF sigma factors are required to survive envelope stress.

Ancestral zinc-finger bearing protein MucR in alpha-proteobacteria: A novel xenogeneic silencer?

“…MucR represses its own transcription [24] , [39] , [41] . A non-comprehensive list of MucR regulon consists of genes involved in synthesis of various exopolysaccharides ( exo , uxs-uxe-aps ) and c-di-GMP signaling components (GGDEF and EAL containing proteins) [26] , [42] , [43] ; machineries of motility & chemotaxis (VisNR, Rem, Fla, Fli, Mcp and Che) [25] , [27] , [28] , [29] , and conjugation & secretion (Pilus, T4SS, T3SS and T1SS) [27] , [28] ; and various transcriptional regulators and signalling components in general stress response (RpoE2, RpoE5 and CspA) [28] , [44] , [45] , cell cycle (CtrA and SciP) [38] , carbon and nitrogen metabolism (PTS Ntr ), uptake of potassium (Kdp), zinc (Znu), phosphorus (Pho, Pst and Phn), iron (Irr, RirA and Afu), molybdenum (Mod) and sulfur (Ssu) [28] , [29] , [46] . Collectively, the MucR regulon is multifaceted in life cycles of diverse alpha-proteobacteria.…”

Metal‐responsive RNA polymerase extracytoplasmic function (ECF) sigma factors

“…Under iron‐depletion, the regulator does not bind the metal, thus preventing Fur from binding to DNA and transcription of the genes involved in iron acquisition often occurs under the control of transcriptional activators. Several iron supply systems are positively regulated by ECF sigma factors that are induced by the availability of specific iron sources (Sexton et al , ; Leoni et al , ; Biville et al , ; Lindeberg et al , ; Thakur et al , ; Chevalier et al , ; Lang et al , ).…”

“…Other FecI homologues, such as FiuR/FiuI, FoxR/FoxI, HasS/HasI and FemR/FemI, are present in many bacterial species belonging to the Proteobacteria phylum. Most of them are often clustered with genes coding for a FecA‐like OMP and a putative anti‐sigma factor containing a FecR‐like domain (Sexton et al , ; Biville et al , ; Braun et al , ; Brooks and Buchanan, ; Thakur, et al , ; Llamas et al , ; Chevalier et al , ; Lang et al , ). The great variety of associated domains, organized in almost 200 different architectures according to the Pfam database (El‐Gebali et al , ), seems to indicate that this FecIR system might be a generalized signal‐transduction mechanism used to regulate the entry of different types of products (Staroń et al , ; Karlsson et al , ; Mascher, ; Pinto and Mascher, ) such as complex polysaccharides in the gut environment, as suggested for FecIR‐like systems in Bacteroidetes (Xu et al , ).…”

Sinorhizobium meliloti Functions Required for Resistance to Antimicrobial NCR Peptides and Bacteroid Differentiation

“… S. meliloti has 11 RpoE-like sigma factors. Remarkably, despite the fact that some RpoEs have a considerable effect on gene transcription, all single mutants, all possible double mutants, and even a mutant lacking all 11 genes showed no detectable phenotypic difference from the wild type in symbiosis or during many tested free-living growth conditions, including growth in the presence of membrane stresses ( 61 , 62 ). Thus, the 11 S. meliloti RpoEs do not have the expected role in regulating the envelope stress response.…”